1. Field of the Invention
This invention relates to an improved magnetic recording medium and to a method for the manufacture thereof. More particularly, this invention relates to a magnetic recording cording medium for use in high-density magnetic recording and to a method for the manufacture thereof.
2. Description of Prior Arts
Generally, magnetic recording media have conventionally been formed by applying to the surface of a non-magnetic substrate a composition obtained by kneading ferromagnetic particles with a binder vehicle. In consequence of increased utilization, the magnetic recording media are now required to have increasingly high density. For the magnetic recording medium of this class to meet this demand, it should satisfy the following requirements:
(1) The ferromagnetic particles should possess high coercive force. PA1 (2) The ferromagnetic particles should possess a high intensity of saturated magnetization I.sub.s. PA1 (3) The ferromagnetic particles should possess small diameters, preferably not more than 0.4 .mu.m major diameter and not more than 0.04 .mu.m minor diameter. PA1 (4) The ferromagnetic particles should be uniformly dispersed in the binder vehicle. PA1 (5) The magnetic film applied to the surface of the non-magnetic substrate should be smooth enough to preclude occurrence of appreciable spacing loss from the magnetic head.
The first three (1), (2), and (3) of the total of five requirements enumerated above have now become feasible owing to the improvement in acicular iron oxide crystals, the development of acicular iron oxide particles having cobalt adsorbed thereon and acicular magnetic alloy particles using iron as a main component. The requirement (4) which calls for uniform dispersion of magnetic particles in the binder vehicle, however, poses a dilemma in that it is impeded by the fulfilment of the requirements (1) through (3).
An object of this invention, therefore, is to provide an improved magnetic recording medium for high-density magnetic recording.
Another object of this invention is to provide a magnetic recording medium for high-density magnetic recording, which has a smooth magnetic film formed on a non-magnetic substrate by the application to the substrate of a composition having very fine acicular magnetic particles of a high coercive force and a high intensity of saturated magnetization uniformly dispersed in a binder vehicle.